Heart disease and malfunction is a major killer of men and women in America A variety of pathologies can affect the beating patterns of a heart, and thereby predispose it to developing ventricular fibrillation. Prior to the occurrence of such a severe and ineffective rhythm, conventional pacemakers can be used to treat, for example, such disorders as sino-atrial (SA) node block, A-V block, and multiple independent sites of contraction in the ventricles (also termed ectopic foci), which, in the extreme, can lead to life threatening ventricular fibrillation. Conventional pacemakers often will control and prevent the recurrence of ectopic foci by preprogrammed stimulation of (usually) the right ventricle via a single electrode. Some pacemakers also employ a second electrode that is dedicated to the left ventricle. In addition, conventional pacemakers utilize a range of circuit logic patterns to counter specific problems that are encountered in the more common pathologies.
However, conventional single ventricular electrode technologies, including the use of a separate single electrode to each ventricle, fail in cases in which ventricular fibrillation has ensued (particularly when the fibrillation is due to multiple random reentry), and single site stimulation does not entrain sufficiently large areas of surrounding tissue to produce the concerted contraction that is necessary for optimal efficiency in pumping blood. In such cases of ventricular fibrillation from multiple random reentry, the patient is put in grave jeopardy for the basic reason that virtually all of the body functions depend on delivery of blood to the tissues in order to supply oxygen and nutrients, and also to carry away metabolic waste products. Failure to correct such a condition, where the rhythm is so far from optimal, results in the patient being in substantial danger of dying in a very short period of time. Though cardioversion/defibrillation may be employed, including that preprogrammed in the control logic for automatic activation in some pacemaker-defibrillators, such protocols typically require large doses of electrical energy to the patient. In addition to producing extreme discomfort and sharp pain, these large doses of electrical energy often also produce cardiac damage. The voltage for standard internal defibrillation/cardioversion is from 150 to 800 volts, corresponding to approximately 10-35 joules.
Several approaches to these problems have been disclosed. One approach is to stimulate greater portions of ventricular myocardium by utilizing larger electrodes so that greater portions of myocardium are simultaneously stimulated. For example, U.S. Pat. No. 5,411,547 to Causey, III discloses the use of defibrillation electrode patches for more efficient bipolar cardiac stimulation. In addition, the use of large, plate-like electrodes for defibrillation and cardioversion is well known. However, the use of such larger electrodes suffers from the problem of delivery of large doses of electrical energy that produce great discomfort to the patient and the possibility of tissue damage.
Yet another approach is to use multiple individual electrodes appropriately placed about the ventricles, as has been disclosed in the following U.S. Pat. Nos. 5,649,966 to Noren. et al., 5,391,185 to Kroll, 5,224,475 to Berg. et al., 5,181,511 to Nickolls, et al., and 5,111,811 to Smits. Though these patents disclose the use of multiple electrodes, they do not disclose or suggest their use for gradually (yet quickly) entraining the various reentrant foci that can exist in pathological ventricles by stimulating in a progressive pattern that mimics the normal wave of depolarization that occurs in the heart.
Thus, a need exists for an anti-reentry apparatus and method that will require the use of less electrical current/voltage than is typically used for defibrillation and cardioversion in order to decrease the likelihood, or at least the severity, of tissue damage. A need also exists for an anti-reentry apparatus and method that will simultaneously stimulate greater portions of ventricular myocardium to increase the probability of ventricular conversion (particularly in the presence of multiple random reentry), but with delivery of lower doses of electrical energy per stimulation, which, consequently, will prolong the life of the apparatus's batteries and decrease myocardial soft tissue damage. A need also exists for such an anti-reentry apparatus and method that not only will produce the vitally needed improvement in cardiac pumping efficiency, but additionally will simultaneously lower the probability of tissue damage, and provide greater comfort for the patient. In addition, a need exists for an anti-reentry apparatus and method that progressively stimulates the ventricles in a manner that mimics the normal cardiac wave of depolarization, thereby providing rapid control and reversion of cardiac rhythm to a normal beating pattern.